| Autor: |
Belik, A. A., Takano, M., Boguslavsky, M. V., Stefanovich, S. Yu., Lazoryak, B. I. |
| Zdroj: |
Chemistry of Materials; January 2005, Vol. 17 Issue: 1 p122-129, 8p |
| Abstrakt: |
New vanadates Sr9R(VO4)7 (R = Tm, Yb, and Lu) were synthesized using a standard solid-state method at 1373 K and found to be isotypic with Ca3(VO4)2 at room temperature (RT). Their structure parameters were refined using the Rietveld method from synchrotron X-ray diffraction (XRD) data measured at RT (space group R3c and Z = 6). Sr9R(VO4)7 (R = Y and La−Er) do not form a phase isotypic with Ca3(VO4)2. Sr9R(VO4)7 (R = Tm, Yb, and Lu) were characterized through the magnetic susceptibility (2−400 K), the specific heat (0.45−31 K), thermal analysis (300−1573 K), and high-temperature XRD, second-harmonic generation, and dielectric measurements. The temperature dependence of the dielectric constant and tangent loss suggested that they exhibit a reversible ferroelectric−paraelectric phase transition of the first order near 950−960 K. The high-temperature phases have space group R&thremacr;m and Z = 3. Thermal analysis revealed the presence of an intermediate phase between the R3c and R&thremacr;m phases in a very narrow temperature range. Magnetic susceptibilities of Sr9Tm(VO4)7 and Sr9Yb(VO4)7 are typical of Tm3+ and Yb3+ ions affected by an octahedral crystal field. The effective magnetic moments were 7.39 μB for Tm3+ and 4.59 μB for Yb3+. |
| Databáze: |
Supplemental Index |
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